Altered cytosolic calcium buffering contributes to arrhythmogenesis in patients with atrial fibrillation

• Applicant: Professor Dr. Wolfgang Niels Voigt
• Subject Area: Pharmacology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 545905905

More than two million people in Germany suffer from atrial fibrillation (AF), the most common arrhythmia in the clinical setting. Current pharmacological treatment options are still largely based on classical antiarrhythmic drugs, which have insufficient efficacy and exert severe side effects. It has been shown that intracellular Ca2+ handling is altered in AF and that this plays a major arrhythmogenic role. It is important to note that only about 1 % of cytoplasmic Ca2+ is free, whereas the rest is buffered. Thus, small alterations in cytoplasmic Ca2+ buffering can have huge implications for Ca2+ dynamics and in the development of arrhythmogenic activity. Cardiac troponin C (cTnC) is a major buffer of cytoplasmic Ca2+ and we and others have shown that cTnC levels are lower in AF. Our preliminary data indicate that Ca2+ buffering is impaired in persistent AF and we hypothesize that this may be due to reduced levels of cTnC. In the present study we aim to build on these findings, determining the consequences of reduced Ca2+ buffering on atrial arrhythmogenesis and in AF pathophysiology. We aim to develop novel therapeutic strategies targeting impaired Ca2+ buffering in AF. We will use various experimental models to investigate our hypothesis that reduced intracellular Ca2+ buffering contributes to AF-associated remodeling. We will collect right atrial tissue samples from patients undergoing open heart surgery, from which we will isolate atrial myocytes and study their physiology and Ca2+ buffering properties. Furthermore, we have established a cTnC knockdown model in human induced pluripotent stem cell-derived cardiac myocytes, thereby providing a model for high-throughput investigation of cellular electrophysiology and the effects of impaired Ca2+ buffering. We will also employ engineered heart muscle models (EHM), in vitro mouse models and a pig model of AF, which will allow us to correlate whole heart electrophysiological data with in vitro findings at the cellular level. In addition, we will perform high-throughput proteome analysis of our experimental models, in order to confirm our initial findings of altered troponin levels in AF. We will correlate protein expression profiles (troponins and other myofilament proteins) with clinical data and also with individual Ca2+ buffering parameters. Finally, we will investigate the effects of Ca2+ sensitizers in the various models to explore whether pharmacologically targeting Ca2+ buffering represents a potential strategy for the treatment of AF. Taken together we will evaluate the potential role of altered Ca2+ buffering in the development of arrhythmogenic activity at the molecular, cellular, tissue and whole organ level. We will employ clinically relevant models that will facilitate translation of our finding into the clinical setting. Ultimately, the insights from this work have the potential establish cytosolic Ca2+ buffering as a novel therapeutic target for treatment of AF.

• DFG Programme: Research Grants